Age resisting vulcanized rubber



Patented Aug. 20, 19 35 time *rr I MEN Torin 7 9 Claims. (01. 18-50 Thepresent invention relates to an-improved process in the vulcanization ofrubber, balata and analogous compounds and th'eproducts obtainedthereby, wherein desirable age resisting properties are'developedin thevulcanized rubber product. i

The invention will be understood from the follow-v ing description andexamples wherein a preferred mode of operating'the invention is fullyset forth anddescribed.

f It is well known'that rubber deteriorates'rapidly when exposed to air,heat and sunlight and that such deterioration is characterized bya lossin the tensile strength; resiliency and other'de sirable properties, ofthe vulcanized rubber prodnot. It has now been'found according'to thepresent invention that such deterioration can be great- 1y lessened ifthere .be incorporated the rubber mix a compound of the classhereinafter set iorth.

I The age resisting characteristics of a vulcanized rubber product canbe readily ascertained by subjecting samples ofthe'yulcanized product toan accelerated aging test'wherein portions of the cured rubber'productare subjected in a bomb to the action of oxygen under pressureand'mainftained for severalhours at an elevated temperature. The treatedsamples a're then examined and tested and the results compared withresults;

similarly obtained by testing the unaged vulcanized rubber stock. Thedeterioration in properties suffered as a result of the oxidationtreatment is indicative of the result that would normally be expectedfrom that particular stock during several years of natural aging Such atest is known as the Bierer-Davis aging test.

Thenewclass of anti-oxidant or age resisting materials which afterincorporation into a rubber stock have been found to impart suchexcellent age resisting qualities to. the vulcanized product I thatportions thereof, whensubjected to the arti-- ficial aging testsdescribed, undergo only a rela-.

tivelysmall loss in modulus tensile strength and other qualities,comprises a reaction product of a hydroxy substituted diphenylalkylidenecompound and an aromatic aminel be prepared'is as follows:

1 "Dihydroxy diphenyl methane was prepared by refluxinga mixtureof'phenol and formaldehyde in the proportion of substantially twomolecular proportions of phenol to substantially one molecularproportion of formaldehyde iorsubstantially 5 i from two to four hoursin the presence of a cat alyst cit-condensing agent; for examplesulfuric acid. After completion of the reaction, the product for-med waspreferably washed first with a weak alkaline solution, for examplea fivepercent 10 sodium hydroxide-Solution, and then with water. The alkaliand water washed material was then Y heated preferably to a temperatureofsubstantially 220 0 whereupon the reaction product after coolingsolidified to a resin, which ground to a nearly white powder lmelting atsubstantially /00 2 0 I Dihydroxy diphenyl methane prepared in themanner hereinbefore set forth and beta naphthyl amine in the ratio ofsubstantially onetmolecular 20 proportion of the former to substantiallya slight excess over two molecular proportions of the latter were heatedin the presence of beta naphthy'l amine hydrochloride for approximately4 to 6 hours at a temperature of substantially 190 to 25 210 C. Afterthe heating was completed,.the reaction product was'washedthoroughlywith boiling water and dried. Asa further means of purification, thefwater-washed product w as washed with hot ethyl alcohol. The productthus obtained: was a solid melting at substantially J 162.0 C. to 166 C.v The product prepared in the manner described above was compounded inthe;

well known manner ina typical rubber treadstock,

comprising r 35" parts ofsmoked sheet rubber v 40 a partsof carbonblack;

; r 10 parts of zinc oxide 325 parts of sulfur A 1 part of diphenylguanidine J 1 part 'anti-qxieant described we 2 parts of avblendedmineral oil and rosin 40 i iv in an oxygen bomb in the manner describedfor 39 hours at a temperature of 70 C. and an oxygen pressure of 300pounds per square inch. A comparison between the tensile and modulusproperties of the aged and unaged vulcanized rubber products is given inTable I.

Table I Cure Modulus of elasticity in at Tensil t Ult' to r e on a ions6 a una Lbs. E break in elongation T me steam g lbs./in. percent mms.pres- 30 4o 0 781 2135' 3000 635 30 40 39 849 1820 1870 500 40 0 12683000 4165 635 60 40 39 1285 2555 2605 510 90 40 0 1650 3560 4520 600 I90 40 39 1490 2575v 480 The data set forth in Table I shows thatavulcanized rubber product wherein there is moor-- porated in the usualmanner-in a v rubber tread stock comprising I 100 parts of smoked sheetrubber 40 parts of carbon black. 10 parts of-zinc oxide 2 parts of ablended mineral oil'and rosin 3.2 5 parts of sulfur 1 part of diphenylguanidine.

1 part of anti-oxidant The rubber stock thus'cOmpQunded was vul-icanized in the usual manner, and portions of the cured rubber productwere artificially aged in V the manner'hereinbefore set forth in anoxygen bombat C. and under an oxygen pressure of 300 pounds per squareinch. A comparison between the. aged and unaged v ulcanize d rubberproduct is set forth in Table II.

Table II Modulus of elasticity in Cure lbs/in. at

elongfations I Y O Tensile at Ultimate Hous break in elongation agelbs/in. percent 'T The.

line s cam mins. pres- 300% 500% sure so 40 0 7'90 2005 .2355 560 30 4039 655 1005 430 60 40 0 1244 3000 4050' 630 60 40 39 976 Z 1498 450 0040 0 1530 3220 3930 580 90 40" 30 1125 1388 380 7 'From the data givenin Table II itis apparent that the reaction product of :dihydroxydiphenyl V methane and alpha naphthyl amine possess the-1 antioxidantproperties ofthe preferredclass of compounds. A stock similar to thatemployed in the foregoing test with the sole exception that noanti-oxidant be used when subjected to the aging test described, meltsto a shapeless mass incapable of test.

A reaction product of substantially one molecular proportion ofdihydroxy diphenyl methane and substantially two molecular proportionsof aniline has also been prepared in a manner analogous to thathereinbefore set forth and on testing in a rubber tread stock was foundto possess anti-oxidant properties characteristic of the class describedherein". '1 f .As a further example of the use of the preferred class ofcompounds, a reaction product of 2,4 tetrahydroxy diphenyl methane andbeta naphthyl amine was prepared in the following manner.

2,4 tetrahydroxy diphenyl methane, prepared from resorcinol andformaldehyde in a manner analogous to that set forth in Berichte derDeutschen Chemischen Gesellschaft, vol. 25,

7 page 947,and beta naphthyl amine in the ratio of substantially onemolecular proportion of the former to an excess over substantially'fourmolecular proportions of the latter were heated for substantially twotofive hours at a temperature 7 of approximately. 190m 200' C. in thepresence of beta naphthyl amine hydrochloride. After the heating of theabove reactants was completed, the reaction product was digested withaquantity of dilu te acid 'for example 10 percent dilute hydrochloricacid, and-then washed with water. thus obtained may be washed with anorganic solvent for exampleethyl alcohol. The material prepared asdescribed was incorporated in a'rubber tread stock comprising The rubberstock thus'compounded was vulcanized vby. heating in a press fordifferent times at the temperature givenby 40 pounds of steam pressureper square inch. Portions of the cured rubber product'were thenartificially aged by heating in a bombfor-39 hours at 70 C. under anoxygen pressure of 300 poundsfper square inch. The tensile data obtainedon testing the aged and unaged vulcanized rubber compound are given inthe following table.

TabZe'III Modulus 01'" elasticity in Cure 1bs./in. at,

- elongations Tensile at Ultimate break in elongation Lb g lbs/in.percent s. Y 1

Time; steam, 32; 522 mms. pres cent cent If convenient or desirable, theproduct.

From the data set forth in Table III it is ap-L' scribed is a darkcolored-resin which was ram s-v parent that the reaction product oi2,4"tetrahydro'xy diphenyl methane and beta naphthyl amine is'anexcellentanti-oxidant and exhibits to a highly satisfactory degree theage resisting qualities of the preferred new class of compounds.

As another example of the use of the pre-' ferred class of compounds,substantially one molecula'r proportion of 2,3 tetrahydroxydi phenyl'metha'ne, prepared byreacting substantially two molecular proportionsof pyrocatechol withsubstantiallyone' molecular proportion offormaldehyde, was reacted with substantially} four molecular proportionsof alpha naphthyl amine in a: manner analogous to that-{by which thereaction product of 2,4 tetrahydroxy diphenyl methane and betanaphthyl-amine, as here'inbefore set forth, was prepared. Theproduct was100 parts of smoked sheet rubber 40 parts of carbon black parts of'zincoxide;

2 parts of a blended mineral oil and rosin v 3.25 parts of sulfur V c =1part of diphenyl guanidine 1 part of anti-oxidant The compounded r ubberstock was then vul-' canized in the well known manner and the curedrubber aged in the oxygen bomb for 39 hours at.

70 .C. and under an oxygen pressure of 300 pounds per square inch.v Theresults of the tests on the aged and unaged vulcanized rubber productsare given in Table IV. l

I As a, furtherexample of the use of the preferred class ofanti-oxidants, 2,4 tetrahydroxy diphenyl methane prepared in the mannerhereinbefore set forth and ortho toluidine in the ratio of substantiallyone molecular proportion of the former to an excess over substantiallyfour molecular proportions of the latter. were heated in the presenceof'a small proportion of acondensing agent or catalyst for exampleiodine for approximately from three to five hours at a temperature ofsubstantially 180 to 200 C. After the reaction was completed theunreacted excess of ortho toluidine was removed by any convenient means,

as for example by steam distillation. The residual product was washedfirst with a dilute aqueous alkali solution, as for example a fivepercent aque-:

ous sodium hydroxide solution, and then with water. The productprepared'in the manner deferred' class of compounds.

rated in a-rubb'er stock comprising p 1 100 parts of smoked sheet rubber40 a parts of carbon black 10 v parts of zinc oxide I 2 arts of ablended mineral oiland rosin 7 3.25 parts of sulfur ,1 part of diphenylguanidine 1 part of anti-oxidant v and'po rtions of the cured rubberproduct aged in the oxygen bomb in the manner hereinbefore set forth for39 hours at 70"" C; and under an oxygen pressure of .300 pounds persquare inch. *The results of the tests of the aged'and unaged vulcanizedrubber product showedthis material to possess antio'x'idantpropertiestypical of the'pre- In allcithe examp s hereinbefore cited, di

phenyl guanidine was employed as an accelerator, bjecauseit is -known toproduce a vulcanized rub,- ber'stockthat imparts exceptionally pooraging qualities to a curedrubber stock and consequently does notmask'the efiec t of the anti-oxidant; Otheraccelerators could, ofcourse, be employed and-"would produce astock possessing differenttensile strengths from those in the examples set forth. Suchstocks,'howeve r, stillpossessed desirable aging characteristics whenthe preferred class of'materials were employed therein. Qtherf hydroxydiphenyl alkylidene compounds than those hereinbefore set forth may bereacted vitith aromatic amines and employed as anti-oxidants; Thus,dihydroxy diphenyl ethane, di-

hydroxy diphenyl. pro-pane, 2,4 tetrahydroxy diphenyl. ethane,-2,4tetrahydroxy diphenyl propane and the like may be reacted with aniline,

alpha'andbeta naphthyl amine and analogous compounds and employed asanti-oxidants in a rubber composition of vulcanization characteristics.Other types of rubber compounds readily apparent to those skilled in theart can likewise be employed in place of r the tread formula set forthin theexamp-les of the process.

Whatis claimed is:

1. The process of producing an age resisting vulcanized rubber productwhich comprises heating rubber and sulfur in the presence of anantioxidant selected from a'group consisting in the reaction product ofone molecular proportion of dihydroxy diphenyl methane heat treated atsub- 10 The compounded rubber stock was vulcanized stantially 220 C. andtwo molecular proportions of an amine selected from beta naphthyl amine,alpha naphthyl amine, and aniline, reaction prodnot of one molecularproportion of 2,4 tetrahydroxy diphenyl methane and four molecularproportions of beta naphthyl amine, reactionproduct of substantially onemolecular proportion of 2,3

. tetrahydroxy diphenyl methane and four molecgroup consisting in thereaction product of one molecular proportion of dihydroxy diphenyl"methane and two molecular proportions of an amine selected from betanaphthyl amine, alpha naphthyl amine, and aniline, reaction product ofonemolecular proportion of 2,4 tetrahydroxy diphenyl methane andfour.molecular proportions of beta naphthyl amine, reaction productpresence of an anti-oxidant selected from a 7 ular proportions of Ialpha naphthyl amine and the reaction productof one'jn'olecula'rproportion of 2,4 tetrahydroxy diphenyl methane-and four molecularproportions of jortho, 'toluidine.

i 3. A composition' of-matter comprising rubber and a condensationproduct of two molecular I proportions of phenol and' one molecularproportion of formaldehyde prod'uced in the presence of an acid catalystheate-d, at a temperature of substantially 220 C.,. said heat treatedcondensationfprogluctfbeing. further reacted with;

s ubstantiall y two molecular proportions iof an amine-selected fro Inthe group consisting. in.

aniline; -.i

beta lli yl' ami eha f la th 'am ile 1 .4. 'A processoif age resistingvul canize drubber product which comprises heating rubber and sulfurinthe presence of an'antioxi- 'dant comprising a reaction product 'of'dihyqroxy rdipheriyl inethane'heat treated iatsubstanquantities withsaid hydrox y grpups;

' 5. A processof produc ing an a el'r'esisting caniked ,rubber' productwhich comprises heating rubber andlsulfurjin the presenceoflanantioxidant comprising a reaction product of dihyclroxy diphenyl meth ane heat treatedlat substantially- 220 C. and substantially two:niolec-H ular proportions of beta naphthylamine;

., v6. The age resisting vulcanized; rubber product of substantially onerinolecularuproportion iof 2,3; tetr'ahydroxy diphenyl methane and-four, molec-" presence of,an antioxidant,comprising a reao- 10 tionproduct oi dihydroxy; diphenyl methane heat treateqi at substantially220 Cr; and substantial- 1y; two \1nolecular. prop ortions pf betanaphthyl amine: 1

' $8. ;The;pro( :'ess of producing' anageresisting 15' vulcanized rubberjpro duct which comprises heating rubber anH sulfur in the presence ofan antioxidantllcoinprisingja reaction productof a dihydro'ggy diphenylalkyliclene compound. heat treated at substantially'22fli C. and anaromatic 20 primaryfamine .insufii'cient "quantity to react in equimolecular quantities with said hydroxy groups. a, a a Y p 9. The ageresisting"vulcanized rubber pro-duct prepared byheating rubber andsulfur in the 5 presence of antioxidant comprising a reaction'pro'duc'tof a dihydroxy, diphenyl a'lkylidene compound heat treated atsubstantially 220 C.

and an aromatic p ri'r'nary amine in sufficient quantity, to react inequi-molecular quantities 30 with said hydroxy groups. 7

' "ROBERT LQSIBLEY,

